46 research outputs found
Extension of Ahmed & Thompson Theory to General Elastic Plane Quasi-Wave Propagation in Textured Polycrystalline Material
In polycrystalline materials, such as columnar grained austenitic weld metal, grain scattering occurs. The extent of the scattering depends on the elastic anisotropy of the grains and the geometric features of the grains and grain boundaries. Therefore these properties have to be incorporated in any theoretical modelling
Letters from William Burnside to Robert Fricke: Automorphic Functions, and the Emergence of the Burnside Problem
Two letters from William Burnside have recently been found in the Nachlass of
Robert Fricke that contain instances of Burnside's Problem prior to its first
publication. We present these letters as a whole to the public for the first
time. We draw a picture of these two mathematicians and describe their
activities leading to their correspondence. We thus gain an insight into their
respective motivations, reactions, and attitudes, which may sharpen the current
understanding of professional and social interactions of the mathematical
community at the turn of the 20th century.Comment: documentclass amsart, 17 page
Site-specific chromatin immunoprecipitation: a selective method to individually analyze neighboring transcription factor binding sites in vivo
<p>Abstract</p> <p>Background</p> <p>Transcription factors (TFs) and their binding sites (TFBSs) play a central role in the regulation of gene expression. It is therefore vital to know how the allocation pattern of TFBSs affects the functioning of any particular gene in vivo. A widely used method to analyze TFBSs in vivo is the chromatin immunoprecipitation (ChIP). However, this method in its present state does not enable the individual investigation of densely arranged TFBSs due to the underlying unspecific DNA fragmentation technique. This study describes a site-specific ChIP which aggregates the benefits of both EMSA and in vivo footprinting in only one assay, thereby allowing the individual detection and analysis of single binding motifs.</p> <p>Findings</p> <p>The standard ChIP protocol was modified by replacing the conventional DNA fragmentation, i. e. via sonication or undirected enzymatic digestion (by MNase), through a sequence specific enzymatic digestion step. This alteration enables the specific immunoprecipitation and individual examination of occupied sites, even in a complex system of adjacent binding motifs in vivo. Immunoprecipitated chromatin was analyzed by PCR using two primer sets - one for the specific detection of precipitated TFBSs and one for the validation of completeness of the enzyme digestion step. The method was established exemplary for Sp1 TFBSs within the <it>egfr </it>promoter region. Using this site-specific ChIP, we were able to confirm four previously described Sp1 binding sites within <it>egfr </it>promoter region to be occupied by Sp1 in vivo. Despite the dense arrangement of the Sp1 TFBSs the improved ChIP method was able to individually examine the allocation of all adjacent Sp1 TFBS at once. The broad applicability of this site-specific ChIP could be demonstrated by analyzing these SP1 motifs in both osteosarcoma cells and kidney carcinoma tissue.</p> <p>Conclusions</p> <p>The ChIP technology is a powerful tool for investigating transcription factors in vivo, especially in cancer biology. The established site-specific enzyme digestion enables a reliable and individual detection option for densely arranged binding motifs in vivo not provided by e.g. EMSA or in vivo footprinting. Given the important function of transcription factors in neoplastic mechanism, our method enables a broad diversity of application options for clinical studies.</p
Ensembles and experiments in classical and quantum physics
A philosophically consistent axiomatic approach to classical and quantum
mechanics is given. The approach realizes a strong formal implementation of
Bohr's correspondence principle. In all instances, classical and quantum
concepts are fully parallel: the same general theory has a classical
realization and a quantum realization.
Extending the `probability via expectation' approach of Whittle to
noncommuting quantities, this paper defines quantities, ensembles, and
experiments as mathematical concepts and shows how to model complementarity,
uncertainty, probability, nonlocality and dynamics in these terms. The approach
carries no connotation of unlimited repeatability; hence it can be applied to
unique systems such as the universe.
Consistent experiments provide an elegant solution to the reality problem,
confirming the insistence of the orthodox Copenhagen interpretation on that
there is nothing but ensembles, while avoiding its elusive reality picture. The
weak law of large numbers explains the emergence of classical properties for
macroscopic systems.Comment: 56 page
Permeability changes induced by electric impulses in vesicular membranes
Neumann E, Rosenheck K. Permeability changes induced by electric impulses in vesicular membranes. Journal of Membrane Biology. 1972;10(1):279-290.Electric impulses were found to cause transient permeability changes in the membranes of vesicles storing biogenic amines. Release of catecholamines induced by electric fields (of the order of 20 kV/cm and decaying exponentially with a decay time of about 150 [mu]sec) was studied, using the chromaffin granules of bovine adrenomedullary cells as a vesicular model system. Far-UV-absorption spectroscopy was applied to determine the amount of catecholamines released from suspended vesicles. A polarization mechanism is suggested for the induction of short-lived permeability changes caused by electric fields. Such transient changes in permeability may possibly represent a part of the sequence of events leading to stimulated neurohumoral secretion